Sulfonylurea herbicides have proven to be particularly effective herbicides and are in worldwide use. Sulfonylureas are water-sensitive and compositions comprising sulfonylureas can be decomposed in storage by even low residual levels of moisture.
The most common method of applying agricultural pesticides involves their dilution in a solvent followed by spraying of the resulting solution or dispersion. Because of the increasing costs of non-aqueous solvents and the toxicity of some of them, formulations involving water-soluble or water-dispersible granules have become increasingly popular.
Conventional methods for the preparation of water-soluble or water-dispersible granules involve fluidized bed or pan granulation techniques or the impregnation of an active pesticide agent on preformed mineral granules. In the fluidized bed or pan granulation techniques, water is added to the formulation in a granulation step which must then be removed in a drying step. The drying, accomplished by means of a stream of heated air, is expensive because it is energy intensive and requires elaborate dust collection equipment. It would be advantageous to avoid the drying step. Granules prepared by fluidized bed or pan granulation are generally sprayable upon dilution while the impregnated compositions are applied mechanically, for example, using spreaders.
Often it is desirable to use mixtures of two or more pesticides of different functions to provide broad spectrum control over a variety of weeds and/or undesirable organisms, for example a mixture of a herbicide and an insecticide. Unfortunately, some of the individual components are physically or chemically incompatible as mixtures, especially in long-term storage. For example, carbamate insecticides are generally unstable in the presence of alkaline components and sulfonylurea herbicides are known to be unstable in the presence of acidic materials as well as moisture. The chemical incompatibility can be due to an impurity present in the complementary pesticide and not the bioactive component itself. For these reasons it would be desirable to have a sprayable, formulated product consisting of particles or granules wherein the active components are physically separated. Canadian Patent No. 589,926 describes herbicides bonded to a core of prilled fertilizers or inert materials by a water-soluble binder. However, these compositions employ and retain high levels of water and are intended for use in dry form by direct application.